David jansson and Steven Smith (1991) studied the effect of fixation on creative design presenting engineering design students with design problems and telling them to generate many designs as possible in 45 minutes. One of the problems was to design an expensive, spill-proof coffee cup. It was specified that the design could not include a or Half the students were assigned to the group and were presented with a sample design like the one in Figure 11.19a, which they were told trated what not to do. Notice that this sample design includes a two features specifically forbidden by the design specifications. Another group straw specification, but did not of students, the control group, was given the same task and a sample design.